IMAGING PATTERN-FORMATION - BRIDGING THE PRESSURE GAP

Two surface-sensitive optical imaging methods, Ellipso-Microscopy for Surface Imaging (EMSI) and Reflection Anisotropy Microscopy (RAM) are introduced. They allow imaging of pattern formation on surfaces, e.g., due to submonolayer coverages of adsorbates, al any arbitrary pressur e. In spatio-temporal pattern formation during heterogeneously catalys ed reactions this bridges the 'pressure gap' between well-defined UHV experiments and 'real catalysis'. For the CO oxidation on Pt(110), the parameter space for pattern formation was extended up to 100 mbar, i. e., by 5 orders of magnitude compared to earlier investigations by Pho to-Emission Electron Microscopy (PEEM) which had to be conducted below 10(-3) mbar. With increasing pressure, the synchronisation mechanisms responsible for the observed pattern showed a gradual shift from reac tion-diffusion to thermal-kinetic coupling unveiling previously unseen features of pattern formation in catalysis.